I lost my keys when i ... (walk) home

1)I lost my keys when i ...(walk)home
2)it was raining while we ... dinner
3)i saw the department stores when i ...(sit)on the bus
4)her phone rang while she ...(talk) to her new boss
5)my friends ...(drive)to work when the heard the news on the radio
6)he...(ride)his bicycle when the cat ran across the road
7)we couldn't go to the beach yesterday because it...(rain)
8)it was a lovely day .the sun was shining and the birds ....(sing) in the trees
9)the tourist lost his camera while he ...(walk)around the city
10)the lorry ...(go) very fast when it hit our car
11)i ...(walk) down the street when it began to rain 
12) at this time last year ,i ...(attend) an english course
13)jim ...(stand)under the tree when he heard an explosion
14)while i ...(study) in my room,my roomates ...(have)a party in the other room
15)mary and i ...(dance) the house when the telephone rang